Pneumatic tobacco classifying apparatus

ABSTRACT

A pneumatic tobacco classifying apparatus wherein a tower contains adjustable walls and a partition defining upper and lower classifying chambers connected by two discrete channels. An adjustable chute admits a mixture of tobacco ribs and tobacco leaf laminae into the range of an accelerating device, such as a driven winnower roller or an air-discharging nozzle, which is mounted in the lower chamber and serves to propel the particles of the mixture across the lower chamber against one of the adjustable walls to thus break up agglomerations of ribs and laminae. An ascending air current entrains the laminae and some ribs into the upper chamber, mainly by way of the channels, whereby the entrained ribs descend mainly by way of the other channel and are again propelled by the accelerating device. The heavier ribs descend immediately into and are evacuated from the bottom zone of the lower chamber. The laminae are separated from the air current after leaving the upper chamber.

United States Patent Wochnowski et al.

[54] PNEUMATIC TOBACCO CLASSIFYING APPARATUS [72] inventors: WaldemarWochnowski; Heinz 'Friebel,

both of Hamburg, Germany [73] Assignee: l-launi-Werke Korber & Co. K.G.,Hamburg, Germany [22] Filed: June 5,1970

[21] Appl. No.: 43,734

[30] Foreign Application Priority Data June 26,1969 Germany ..P 19 32312.7

[52] U.S.Cl. ..209/138,209/l49,209/153, 209/154 [51] 1nt.Cl ..B07b7/0l[58] FieldofSearch ..209/l33T,136-141, 209/153, 154; 131/110, 146

[56] References Cited UNITED STATES PATENTS 393,981 12/1888 Hunter..209/l39R 971,608 10/1910 Hedfeldt ..209/137 2,173,088 9/1939 Eissmann...209/l39R 2,600,965 6/1952 Brandau et al ..209/ 139 R 151 3,655,043[451 Apr.l1,1972

2,988,213 6/1961 Davisetal. ..209/21 3,010,576 11/1961 l-larteetal..209/154 3,397,782 8/1968 Kwongetal. ..209/141x 3,608,716 9/1971.Rowelletal. ..209/l39R Primary Examiner-Tim R. Miles AssistantExaminer-Ralph J. Hill Attorney-Michael S. Striker [57] ABSTRACT Apneumatic tobacco classifying apparatus wherein a tower containsadjustable walls and a partition defining upper and lower classifyingchambers connected by two discrete channels. An adjustable chute admitsa mixture of tobacco ribs and tobacco leaf laminae into the range of anaccelerating device, such as a driven winnower'roller or anair-discharging nozzle, which is mounted in the lower chamber and servesto propel the particles of the mixture across the lower chamber againstone of the adjustable walls to thus break up agglomerations of ribs andlaminae. An ascending air current entrains the laminae and some ribsinto the upper chamber, mainly by way of the channels, whereby theentrained ribs descend mainly by way of the other channel and are againpropelled by the accelerating device. The heavier ribs descendimmediately into and are evacuated from the bottom zone of the lowerchamber. The laminae are separated from the air current after leavingthe upper chamber.

18 Claims, 2 Drawing Figures PATENTEDAPR 1 1 1972 m RUM I! 4/ mum hm myV A N n 4 PNEUMATIC TOBACCO CLASSIFYING APPARATUS BACKGROUND OF THEINVENTION The present invention relates to classifying apparatus forfibrous materials, and more particularly to improvements in pneumatictobacco classifying apparatus. Still more particularly, the inventionrelates to improvements in classifying apparatus of the type whereinlaminae and other lighter particles are segregated from a mixture oflighter and heavier tobacco particles by one or more ascending currentsof air.

A pneumatic tobacco classifying apparatus normally comprises a chamberfor an ascending air current and a feeding mechanism which delivers intothe chamber a mixture of lighter and heavier tobacco particles,particularly a mixture of tobacco leaf laminae and tobacco ribs. Thelaminae are entrained by and leave the chamber with the air currentwhereas the ribs descend by gravity and can be evacuated from the bottomzone of the chamber.

A drawback of such apparatus is that heavier laminae are likely toremain admixed to the ribs as well as that smaller fragments of ribsrise with and remain admixed to laminae. Also, those ribs which continueto adhere to relatively large laminae are likely to rise with the aircurrent and to remain admixed to the lighter fraction. Such ribs arelikely to float in the separating chamber to thereby reduce theefficiency of the apparatus. Unsatisfactory segregation of ribs fromlaminae affects the quality of cigarettes or other tobacco-containingproducts. For example, a piece of a rib can puncture the wrapper of acigarette so that the latter cannot pass the customary test for thepresence or absence of leaks and must be discarded.

Certain presently known classifying apparatus are capable of effectivelyseparating lighter particles from heavier particles so that the thussegregated lighter particles contain a relatively small percentage ofheavier particles. Certain other known apparatus are designed to preventremoval of lighter particles with heavier particles but are lesssatisfactory in other respects, particularly in that the removed lighterparticles contain arelatively high percentage of ribs. For example, U.S.Pat. No. l,9 45,77l to Dahlstrom et al. discloses an'apparatus whereinthe mixture of lighter and heavier tobacco particles is fed by a shakertable to enter an ascending air current which permits the heaviestparticles to descend, which entrains the lightest particles, and whichlifts the particles of medium weight to a certain level so that they canreturn onto the shaker table. A drawback of such apparatus is that theycannot break up agglomerations of lighter and heavier particles and thattheir efficiency is rather low, especially if the mixture contains arelatively high percentage of coherent particles. The agglomerationsleave the apparatus with the heaviestparticles so that the heaviestparticles must be subjected to at least one secondary separating action.Moreover, the particles of medium weight are caused to circulate in theapparatus again and again to thus affect the quality of the classifyingaction and the output.

U.S. Pat. No. 2,988,213 to Davis et al. discloses a classifyingapparatus wherein the housing of the classifier contains an uprightpartition which divides the classifying chamber into two compartments.The mixture of lighter and heavier particles is to be loosened by astream of air flowing across the particles which are admitted by aconventional conveyor belt. The air stream is drawn into the housing ofthe separator by suction. The lighter particles rise in one of thecompartments .and the heavier particles return onto the belt in theother compartment. The apparatus also comprises a dust extractor. It wasfound that such apparatus share the disadvantages of the Dahlstromclassifier, mainly because they are also incapable of breaking upagglomerations of coherent tobacco leaf laminae and ribs.

U.S. Pat. 3,164,548 to Rowell et al. discloses a further classifyingapparatus wherein a paddle wheel admits a mixture of lighter and heaviertobacco particles into a chamber wherein the lighter particles areimmediately entrained by a rising cur- SUMMARY OF THE INVENTION Anobject of the invention is to provide a pneumatic tobacco classifyingapparatus which is capable of effectively breaking up accumulations ofcoherent lighter and heavier tobacco particles prior to and in thecourse of separation of lighter particles from heavier particles.

Another object of the invention is to provide a classifying apparatuswhose efficiency is higher than that of presently known apparatus. I

A further object of the invention is to provide an apparatus whoseclassifying action can be regulated in a number of ways to insure anoptimum classification of each of many types of mixtures of lighter andheavier tobacco particles.

An additional object of the invention is to provide a novel and improvedtower for use in a pneumatic tobacco classifying apparatus.

An ancillary object of the invention is to provide a novel device forbreaking up accumulations of coherent lighter and heavier tobacco.particles in a pneumatic tower type tobacco classifying apparatus.

The invention is embodied in an apparatus for segregating lighterparticles from a mixture of lighter and heavier tobacco particles, suchas a mixture of ribs and tobacco leaf laminae. The apparatus comprisesan upright tower or another suitable housing provided with an upper anda lower classifying chamber and a pair of channels connecting the twochambers, feeding means for admitting into the lower chamber a mixtureof lighter and heavier'tobacco particles, air circulating means forconveying through the housing a current of air flowing upwardly from thelower chamber, mainly through one of the channels, and into and from theupper chamber, and accelerating means provided in the lower chamber topropel the particles of the mixture admitted by the feeding means acrossthe air current and preferably against an adjustable wall in the housingwhereby the air current entrains lighter tobacco particles andsomeheavier particles but permits the remaining heavier particles to descendin the lower chamber by gravity. The heavier particles which areentrained by the ascending air current are decelerated and deflected onentry into the upper chamber to descend, at least in part, by way of theother channel which delivers the descending heavier particles into therange of the accelerating means.

7 The accelerating means may include a mechanical accelerating device,e.g., a winnower roller which can be driven at several speeds, or apneumatic accelerating device, for example, a single nozzle or severalnozzles having one or more rows of air-discharging orifices. Theaccelerating action can be regulated by adjusting the feeding means, byadjusting the position of the accelerating device and/or by adjustingthe force with which the accelerating device acts on the particles ofthe mixture. The accelerating device effectively breaks up accumulationsof lighter and heavier particles and it also contributes to separationof such heavier particles which are still attached to tobacco leaflaminae.

The novel features which are considered as characteristic of theinvention are set forth in particular in the appended claims. Theimproved classifying apparatus itself, however, both as to itsconstruction and its mode of operation, together with additionalfeatures and advantages thereof, will be best understood upon perusal ofthe following detailed description of certain specific embodiments withreference to the accompanying drawing.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a schematic partlyelevational and partly sectional view of a classifying apparatus whichemploys a mechanical accelerating device; and

FIG. 2 is a fragmentary sectional view of a classifying apparatus with apneumatic accelerating device.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring first to FIG. 1,there is shown a pneumatic classifying apparatus which segregateslighter tobacco particles from heavier tobacco particles, particularlytobacco leaf laminae from a mixture which contains such laminae andribs, birds eyes and like heavier parts. The apparatus comprises aclassifier proper l which includes an upright housing or tower 7 havingat its top a passageway 49 connected with a removing unit 3 for lighterparticles and by way of the removing unit 3 to an air circulating or airmoving device here shown as a blower 6. Air which is to be returned tothe classifier 1 is relieved of a certain amount of dust by a dustextractor 4. A feeding unit 2 is provided to deliver a mixture oflighter and heavier tobacco particles into the interior of the housing7. The latter contains an adjustable partition or divider 11 which isdisposed between an upper classifying chamber 8 and a lower classifyingchamber 9 of the housing 7. These chambers communicate with each otherby way of two discrete channels, l2, 13 which flank the partition 11.The volume of the chamber 8, 9 and of the channels 12, 13 can beadjusted by movable internal walls 14, 16 and 17 which are installed inthe housing 7 and can be adjusted from without to select an optimumcross-sectional area for the channels 12, 13 as well as an optimumcapacity for the chambers 8, 9. The adjusting means for the movablewalls 14, 16 and 17 are respectively shown at 21, 18 and 19. Thepartition 11 is pivotable with a horizontaladjusting shaft 22 which canbe manipulated from the outer side of the housing 7 and serves as ameans to adjust the crosssectional areas of the channels 12, 13. In theillustrated embodiment, an angular adjustment of the partition 11 aboutthe axis of the shaft 22 will result in an increase in thecross-sectional area of the channel 12 at the expense of thecross-sectional area of the channel 13, or vice versa. The mode ofoperation of the adjusting means 18, 19 and 21 will be self-evident byreferring to FIG. 1. It suffices to say that each of the movable walls14, 16, 17 preferably comprises two or more articulately connectedsections or panels which can be adjusted with as well as relative toeach other. Certain adjusted positions of the movable walls 14, I6, 17are indicated in FIG. 1 by phantom lines but it is clear that each ofthese walls can be moved to a practically infinite number of positionsother than those shown by solid and phantom lines.

The feeding unit 2 includes a belt conveyor 23 whose discharge end istrained around a roller 23a and which delivers a stream of intermixedlighter and heavier tobacco particles in the direction indicated byarrow 53. The particles of the mixture descend (arrow 54) into ametering device here shown as an air lock 24 including a paddle wheelwhich at least reduces the amounts of air entering the interior of thehousing 7 and which feeds a practically continuous stream of tobaccoparticles (arrow 56) onto an adjustable chute 26 whose inclination canbe regulated from without to change the direction of entry of themixture and the manner in which the particles of the mixture are causedto move in and across the lower classifying chamber 9. It will be notedthat the discharge end of the air lock 24 communicates with the housing7 at a level below the partition 11 so that the mixture invariablyenters the lower classifying chamber 9.

In accordance with a feature of the invention, the feeding unit 2further includes a driven winnower roller 27 which constitutes amechanical propelling or accelerating means and is disposed adjacent tothe discharge end of the chute 26 close to the movable wall 16 to propelthe particles of the mixture across the lower classifying chamber 9 in adirection toward the lowermost section or panel 14a of the movable wall14.

The air intake of the blower 6 draws a current of air from the removingunit 3 by way of a return conduit 33 (arrow 64) provided with an airadmitting gate or valve 34 which is ad justable to deliver into thereturn conduit 33 as much air as is necessary to compensate for leakageand losses due to extraction of dust in the unit 4. The outlet of theblower 6 discharges a current of air into a supply conduit 36 containingan adjustable air quantity regulating valve 39 and having a branch 41containing a second adjustable regulating valve 42. The branch 41 isconnected with the inlet of the dust extractor 4. The supply conduit 36has two outlets 37, 38 which admit air to different zones in theinterior of the housing 7. The outlet 36 discharges the major part ofthe air current into a compartment 43 which is bounded by the bottomwall and a portion of one side wall of the housing 7 as well as by thelowermost panel 14a of the movable wall 14. The panel 14a is providedwith a large number of apertures or orifices which admit discretecurrents of air (arrows 51) into the lower classifying chamber 9. Themovable wall 16 forms with the panel 14a a funnel which divergesupwardly toward the partition 11 and flanks the lower chamber 9. Theother outlet 38 of the supply conduit 36 discharges a relatively smallamount of air into a second compartment 44 which is bounded by a portionof the bottom wall and a portion of another side wall of the housing 7as well as by the sections or panels of the movable walls 16, 17. Thewall 16 is also formed with apertures or orifices which admit discretecurrents of air (arrows 52) into the adjacent portion of the lowerclassifying chamber 9 in the region below the winnower roller 27.

The bottom wall of the housing 7 has a substantially centrally locateddischarge opening above a cell wheel 48 which evacuates the heavierparticles entering the cell wheel in the directions indicated by arrows58. The cell wheel 48 discharges heavier particles into a collectingreceptacle (not shown) or onto a takeoff conveyor. This cell wheel isflanked by the lowermost panels of the movable walls 14 and 16.

The lighter particles leave the upper classifying chamber 8 through thepassageway 49 (arrow 62) and accumulate in the bottom portion of theseparating unit 3 to leave the latter by way of a revolving cell wheel46 (arrow 63) and to enter a discharging pipe 47 which delivers lighterparticles to a second collecting receptacle (not shown) or to a secondtakeoff conveyor which advances such particles to a further processingstation, for example, to a cutting machine which forms shred for use inthe manufacture of cigarettes.

The operation:

The motor 6a which drives the blower 6 is started and the valves 34, 39,42 are adjusted to circulate a current of air at an optimum rate throughthe supply conduit 36, through the outlet's 37, 38 and compartments 43,44 (arrows 51 and 52), thereupon upwardly through the lower classifyingchamber9, mainly through the channel 12, upwardly through theclassifying chamber 8, through the passageway 49, through the separatingunit 3 and by way of the return conduit 33 (arrow 64) back to the blower6. The motor 6a can also serve to drive the winnower roller 27 in aclockwise direction, to drive the air lock 24 and cell wheels 48, 46and/or to operate the movable parts of the dust extractor 4. Theoperator also adjusts the movable walls l4, 16, 17 (if necessary) by wayof the adjusting means 21, l8, 19 so as to select a propercross-sectional area for the classifying chambers 8, 9 and channels 12,13. If necessary, the operator also adjusts the position of thepartition 11 by changing the angular position of the shaft 22.

The conveyor belt 23 is thereupon started to deliver a substantiallycontinuous stream of a mixture of lighter and heavier tobacco particlesin the direction indicated by the arrow 53. Such mixture descends at thedischarge end of the belt 23 (arrow 54) and enters the air lock 24 whosepaddle wheel transfers metered quantities of the mixture onto the chute26 whereby the resulting stream descends along an inclined path (arrow56) and into the range of the revolving blades of the winnower roller27. These blades accelerate the particles and propel them across thelower classifying chamber (arrows 57) in a direction toward thelowermost panel 14a of the movable wall 14. The panel permits passage ofdiscrete air currents (arrows 51) which entrain the lighter particlesinto and through the right-hand channel 12 (arrows 59). The blades ofthe winnower roller 27 perform the additional important function ofbreaking up agglomerations of lighter and heavier tobacco particles sothat the lighter particles can be readily entrained by air to passthrough the channel 12 and to rise in the upper classifying chamber 8toward the passageway 49.

The ribs and other heavier particles of the mixture which is propelledby the blades of the winnower roller 27 are caused to impinge againstthepanel 14a and descend by gravity (arrows 58) into the cell wheel 48.The heaviest particles need not even reach the panel 14a; they candescend by gravity without any impact against the movable wall 14. Theadjustability of the chute 26 is important because the operator is in aposition to change the inclination of the path along which the mixturetravels toward the blades of the winnower roller 27. Thus, depending onthe consistency of the mixture (the percentage of agglomerated orcoherent lighter and heavier particles, the moisture content of themixture, the percentage of ribs, and/or other factors), the paths alongwhich the particles of the mixture are propelled across the lowerclassifying chamber 9 can be selected in such a way that the apparatussegregates a very high percentage of lighter particles.

The air currents which enter the lower classifying chamber 9 by way ofthe panel 14a and movable wall 16 (arrows 51 and 52) immediately entrainthe lighter tobacco particles so that such particles cannot enter thecell wheel 48. The ascending air is likely to entrain certain heavierparticles, particularly those ribs which adhere to laminae. Such heavierparticles enter the upper chamber 8 but are too heavy to rise to theinlet of the passageway 49. Thus, they descend in the chamber 8 andreturn into the range of the blades on the winnower roller 27 whichpropels them toward the panel 14a to effect a secondary classification.The advantageous feature of the apparatus that the heavier particleswhich have entered the upper chamber 8 descend by way of the channel 13rather than by way of the channel 12 and are thereby returned into therange of the winnower roller 27 is due to the fact that the quantity ofair admitted by the outlet 38 is less than the quantity of air enteringthe compartment 43 and chamber 9 by way of the outlet 37. The lesserquantity of air which is admitted by way of the outlet 38 forms acurrent which ascends mainly in the lefthand channel 13 and the largerquantity of air admitted by way of the outlet 37 rises mainly in thechannel 12. Therefore, a pressure differential develops between theupper ends of the channels 12, 13 with the result that the heavierparticles which happen to enter the upper chamber 8 seek the path ofleast resistance and move across this chamber (arrows 61) to descend inthe channel 13 toward the winnower roller 27. The latter is preferablymounted close to the upper portion of the movable wall 16. It was foundthat repeated acceleration of heavier particles which descend by way ofthe channel 13 insures a practically complete breakup of agglomerationsso that the percentage of segregated lighter particles is very high. Thecirculation of some heavier particles around the partition 11 can berepeated more than once, as long as such particles are too heavy toenter the passageway 49 but light enough to be entrained into the upperclassifying chamber 8.

The lighter particles which enter the passageway 49 advance in thedirection indicated by the arrow 62 and descend into the lower zone ofthe removing unit 3 to be evacuated by way of the cell wheel 46 (arrow63) and to enter the discharging pipe 47. The manner in which thelighter particles of tobacco leaves are separated from air is well knownand, therefore, the exact construction of the removing unit 3 forms nopart of the present invention. The air current flows in the directionindicated by the arrow 64 and enters the intake of the blower 6. It willbe noted that the air circulating system of the apparatus defines apractically closed path for the flow of an air current upwardly throughthe housing 7 to insure economical utilization of moving air. The valve34 admits some air to compensate for leakage in the air circulatingsystem as well as for the amounts of air which are caused to passthrough the dust extractor 4.

The drive for the winnower roller 27 preferably includes avariable-speed transmission or a variable-speed motor to enable theoperator to vary the rotational speed of the blades.

The efficiency of pneumatic classifying apparatus depends to a highdegree on the extent to which the accumulations of lighter and heavierparticles are broken up not later than at the time when they enter theascending air current. The winnower roller 27 has been found toconstitute an effective accelerating device which breaks up all ornearly all accumulations as soon as they enter the lower classifyingchamber. The elimination of accumulations is due in part to impace ofparticles against the rapidly revolving blades and/or teeth of thewinnower roller and also to the fact that the particles impinge againstthe panel 14a. Moreover, the particles which are propelled by the bladesof the winnower roller 27 travel along different paths, depending on thepoints of impact against the blades and on the weight of particles, tothus insure a highly satisfactory segregation of a substantialpercentage of lighter particles in the lower classifying chamber 9. Thelighter particles which reach the panel 14a are prevented fromdescending into the cell wheel 48 by currents of air (arrows 51) whichenter the chamber 9 by way of perforations in the movable wall 14.

It was found that the major percentage of lighter particles issegregated from ribs before such lighter particles leave the lowerclassifying chamber 9. Also, a high percentage of ribs descends into thecell wheel 48 without even entering the channels 12 and 13. Theremaining ribs are thereupon decelerated and deflected (arrows 61) toreturn into the range of the winnower roller 27 and to be propelledtoward the panel 14a with the result that they leave the apparatus byway of the cell wheel 48. The particles entering the upper chamber 8 aresubjected to an effective secondary classifying action with the resultthat only the laminae are permitted to leave the housing 7 by way of thepassageway 49 and that the percentage of laminae in the stream ofheavier particles leaving the chamber 9 by way of the cell wheel 48 isvery low. 7

The air lock 24 of the feeding unit 2 can be replaced with anothertobacco metering device without departing from the spirit of ourinvention. Metering of the mixture is desirable because the quality ofthe classifying action is affected if the mixture is admitted at a ratewhich fluctuates within a wide range.

FIG. 2 illustrates a portion of a second apparatus wherein theaccelerating means for the mixture of lighter and heavier tobaccoparticles comprises an adjustable pneumatic accelerating deviceincluding at least one elongated nozzle 128 which is tumably mounted ona shaft 129 and discharges jets of compressed air into the lowerclassifying chamber 109. The nozzle 128 receives compressed air by wayof a flexible hose 132 containing a regulating valve 131. All otherparts of the apparatus shown in FIG. 2 are preferably identical oranalogous to the parts of the apparatus shown in FIG. 1 and certain ofsuch parts are denoted by similar reference characters plus 100. Forexample, the reference characters 113, 144 respectively denote theleft-hand channel and the compartment behind the movable walls 116, 117.The hose .132 is connected to a source of compressed air, not shown,such as a pump or compressor.

The operation of the apparatus shown in FIG. 2 is also analogous to thatof the first apparatus. In this embodiment of our invention, the forcewith which the particles of the mixture admitted by the adjustable chute126 (along the inclined path indicated by the arrow 156) can beregulated by changing the inclination of the chute, by changing theangular position of the nozzle 128 and/or by adjusting the valve 131.

An important advantage of the classifying apparatus shown in FIGS. 1 and2 is that they can break up agglomerations of lighter and heaviertobacco particles with greater efficiency and more rapidly thanpresently known apparatus. Such elimination of agglomerations insuresthat the apparatus can segregate a high percentage of lighter particlesand that the material leaving the apparatus by way of the cell wheel forthe heavier particles (see the cell wheel 48 of FIG. 1) contains littleor no lighter particles. It was found that the percentage of lighterparticles which leave the apparatus with the heavier particles is sosmall that such material need not be subjected to a secondaryclassifying action. The same holds true for lighter particles which arecaused to leave the upper classifying chamber.

Without further analysis, the foregoing will so fully reveal the gist ofthe present invention that others can, by applying current knowledge,readily adapt it for various applications without omitting featureswhich fairly constitute essential characteristics of the generic andspecific aspects of our contribution to the art and, therefore, suchadaptations should and are intended to be comprehended within themeaning and range of equivalence of the claims.

What is claimed as new and desired to be protected by Letters Patent isset forth in the appended claims.

1. Apparatus for segregating lighter particles from a mixture of lighterand heavier tobacco particles, comprising a housing provided with anupper and a lower classifying chamber and a pair of channels connectingsaid chambers; air circulating means for conveying through said housinga current of air flowing from said lower chamber mainly through one ofsaid channels and into and from said upper chamber; feeding means foradmitting into said lower chamber below the other of said channels amixture of lighter and heavier tobacco particles; and accelerating meansprovided in said lower chamber underneath said feeding means to propelthe particles of the admitted mixture across the air current whereby theair current entrains lighter particles and some heavier particles butpermits the remaining heavier particles to descend in said lower chamberby gravity, the entrained heavier particles being decelerated on entryinto said upper chamber to descend, at least in part, by way of saidother channel.

2. Apparatus as defined in claim 1, wherein said accelerating meanscomprises a mechanical accelerating device.

3. Apparatus as defined in claim 1, wherein said air circulating meansincludes a foraminous wall provided in said lower classifying chamberadjacent to said accelerating means.

4. Apparatus as defined in claim 1, wherein said accelerating meanscomprises a rotary winnower.

5. Apparatus as defined in claim 1, wherein said feeding means comprisesa chute defining an inclined path for directing the mixture of lighterand heavier tobacco particles into the range of said accelerating means,a conveyor for supplying a stream of such mixture, and a metering devicefor transferring the particles of said mixture at a substantiallyconstant rate from said conveyor to said chute.

6. Apparatus as defined in claim 5, wherein said chute is adjustable soas to change the inclination of said path.

7. Apparatus as defined in claim 1, wherein said accelerating meanscomprises a pneumatic accelerating device.

8. Apparatus as defined in claim 7, wherein said pneumatic acceleratingdevice comprises at least one adjustable air discharging nozzle.

9. Apparatus as defined in claim 1, wherein said housing includespartition means disposed at a level between said chambers and flanked bysaid channels.

10. Apparatus as defined in claim 9, further comprising means foradjusting the position of said partition means.

11. Apparatus as defined in claim 1, further comprising movable wallsprovided in said housing and means for adjusting the positions of saidwalls with reference to said housing to thereby change the cross-sectionof at least one of said chambers and at least one of said channels.

12. Apparatus as defined in claim 1, wherein said air circulating meanscomprises supply conduit means having two airadmitting outletscommunicating with spaced portions of said housing to admit said aircurrent into said lower chamber.

13. Apparatus as defined in claim 12, wherein one of said outlets admitsair in quantities exceeding those admitted by the other of said outlets.

14. Apparatus as defined in claim 12, further comprising air permeablewalls provided in said housing between said lower chamber and saidoutlets.

15. Apparatus as defined in claim 14, wherein said walls diverge towardsaid upper chamber and flank said lower chamber.

16. Apparatus as defined in claim 1, wherein said air circulating meanscomprises conduit means receiving said air current from said upperchamber and admitting said air current to said lower chamber and meansfor moving the air current through said conduit means.

17. Apparatus as defined in claim 16, further comprising means forremoving lighter tobacco particles from the air current in said conduitmeans.

18. Apparatus as defined in claim 17, wherein the means for moving theair current comprises a blower and said removing means is disposedupstream of said blower.

1. Apparatus for segregating lighter particles from a mixture of lighterand heavier tobacco particles, comprising a housing provided with anupper and a lower classifying chamber and a pair of channels connectingsaid chambers; air circulating means for conveying through said housinga current of air flowing from said lower chamber mainly through one ofsaid channels and into and from said upper chamber; feeding means foradmitting into said lower chamber below the other of said channels amixture of lighter and heavier tobacco particles; and accelerating meansprovided in said lower chamber underneath said feeding means to propelthe particles of the admitted mixture across the air current whereby theair current entrains lighter particles and some heavier particles butpermits the remaining heavier particles to descend in said lower chamberby gravity, the entrained heavier particles being decelerated on entryinto said upper chamber to descend, at least in part, by way of saidother channel.
 2. Apparatus as defined in claim 1, wherein saidaccelerating means comprises a mechanical accelerating device. 3.Apparatus as defined in claim 1, wherein said air circulating meansincludes a foraminous wall provided in said lower classifying chamberadjacent to said accelerating means.
 4. Apparatus as defined in claim 1,wherein said accelerating means comprises a rotary winnower. 5.Apparatus as defined in claim 1, wherein said feeding means comprises achute defining an inclined path for directing the mixture of lighter andheavier tobacco particles into the range of said accelerating means, aconveyor for supplying a stream of such mixture, and a metering devicefor transferring the particles of said mixture at a substantiallyconstant rate from said conveyor to said chute.
 6. Apparatus as definedin claim 5, wherein said chute is adjustable so as to change theinclination of said path.
 7. Apparatus as defined in claim 1, whereinsaid accelerating means comprises a pneumatic accelerating device. 8.Apparatus as defined in claim 7, wherein said pneumatic acceleratingdevice comprises at least one adjustable air discharging nozzle. 9.Apparatus as defined in claim 1, wherein said housing includes partitionmeans disposed at a level between said chambers and flanked by saidchannels.
 10. Apparatus as defined in claim 9, further comprising meansfor adjusting the position of said partition means.
 11. Apparatus asdefined in claim 1, further comprising movable walls provided in saidhousing and means for adjusting the positions of said walls withreference to said housing to thereby change the cross-section of atleast one of said chambers and at least one of said channels. 12.Apparatus as defined in claim 1, wherein said air circulating meanscomprises supply conduit means having two air-admitting outletscommunicating with spaced portions of said housing to admit said aircurrent into said lower chamber.
 13. Apparatus as defined in claim 12,wherein one of said outlets admits air in quantities exceeding thoseadmitted by the other of said outlets.
 14. Apparatus as defined in claim12, further comprising air permeable walls provided in said housingbetween said lower chamber and said outlets.
 15. Apparatus as defined inclaim 14, wherein said walls diverge toward said upper chamber and flanksaid lower chamber.
 16. Apparatus as defined in claim 1, wherein saidair circulating means comprises conduit means receiving said air currentfrom said upper chamber and admitting said air current to said lowerchamber and means for moving the air current through said conduit means.17. Apparatus as defined in claim 16, further comprising means forremoving lighter tobacco pArticles from the air current in said conduitmeans.
 18. Apparatus as defined in claim 17, wherein the means formoving the air current comprises a blower and said removing means isdisposed upstream of said blower.